SU1659756A1 - Bulk medium cubic strain measurement process - Google Patents

Abstract

This invention relates to instrumentation engineering and is intended to measure volumetric strain (pressure) fields in bulk media. The purpose of the invention is to measure volumetric strain in bulk media in simulating the behavior of rocks under conditions of a complex stress state. To do this, in the selected location of the test medium 4, in the process of preparing a model sample, a cavity is cut, filled with an electrically conductive material 3, for example, a graphite powder of a given consistency, and an electrically conductive plate 1 is pasted onto the dielectric plate 2. two maximum diameters of the dielectric plate; in this case, the material resistance depends only on the distance between the plates and the bulk strain. During deformation, the resistor is measured and, based on the calibration curve, the volumetric strain is determined. To improve the measurement accuracy, the mechanical characteristics of the resistor material are consistent with the similar characteristics of the granular medium. 2 Il. cl

Description

This invention relates to instrumentation engineering and is intended to measure volumetric strain (pressure) fields in bulk media.

The purpose of the invention is to measure volumetric strain in bulk media in simulating the behavior of rocks under conditions of a complex stress state.

FIG. 1 shows a scheme for implementing a method for measuring volumetric strain; in fig. 2 - calibration graph of the relative resistance of the sensor

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dR

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R -RO

from relative

pressure changes in the P-Ro environment

Ro

(Ro, R - initial and current

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VI

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about

resistance, P0, P - initial and current pressure).

The circuit contains electrically conductive plates 1, a dielectric plate 2, graphite powder 3, and a flowing medium 4.

The method of measuring the volumetric strain (pressure) in the granular medium is implemented as follows.

In the required place of the medium (sand) in the process of preparing the model sample, a cavity is made (notch, 10 mm deep and 10 mm in diameter), filled with its electrically conductive material (graphite powder). Electrically conducting plates (3 x 3 x 0.1 mm in size, made of brass foil) are glued onto a dielectric plate (3x3x1 mm in size) on two opposite sides, to which thin insulated conductors (0.05 mm) are soldered to connect with the measuring apparatus. The contacts thus collected are placed in a hollow filled with graphite powder and covered with sand. The maximum cavity diameter must not be less than 2-3 maximum diameters of the dielectric plate so that the electrical resistance of the electrically conductive material depends only on the distance between the electrically conductive plates and the volume deformation. If necessary, another resistor is formed to another location, and so on. During the deformation of the sample under study, the resistance of the resistor thus obtained is measured. This resistance depends only on the contact density in the electrically conductive material, i.e., on the bulk strain (pressure) in the area. By changing the measured resistance based on the calibration graph shown in FIG. 2, volumetric strain (relative pressure change) in the area of the sensor is judged. The strain sensitivity of the sensor obtained by the method described is 0.35-0.05.

Due to the flowability of the sensitive element material, the behavior of the resistor during deformation is determined by the same laws as the behavior of the medium under study. The absence of a shell allows you to avoid the arched effects and slippage of the sensor body relative to the environment.

The conductive material for the resistor must meet certain requirements. The average particle size of the conductive material must not exceed the average particle size of the test medium, otherwise the density of contacts between the particles in the resistor will be less than in the medium, which will reduce the sensitivity and accuracy of the sensor. Coupling (tear strength) in an electrically conductive material is not

must exceed the adhesion in the test medium so that the deformation of the sensor monitors the deformation of the medium, thus ensuring the required accuracy. In addition to meeting the clutch ratio, it is necessary that the overall compression module of the used electrically conductive sensor material does not exceed the comprehensive compression module

medium, i.e., so that the resistor is not a hard switch. A sensor that is softer than the medium during manufacture and installation will seal to the rigidity of the medium, which is also necessary to improve measurement accuracy.

The combination of these conditions is sufficient to ensure reliable and accurate measurements of volumetric strain, (pressure) of the flowing medium,

Claims (1)

adequate to the process under study. The invention of the method for measuring the volumetric strain of granular media, which consists in placing it in the medium of a resistor, measuring it resistance and determination of the change in the resistance of the sought-after deformations, characterized in that, in order to provide measurements of volumetric deformations in bulk media in the simulation behavior of rocks in conditions of complex stress state, before being placed in the medium of a resistor, a cavity is made in the medium, filled with its loose conductive material, inserted into it two flat contacts placed on a dielectric plate, wherein the characteristics of the electrically conductive material are related to the characteristics of the granular medium by the following relations: BEM dc.c Em  Ss Sam. 5S GC.C., where BEM - the average grain size of the electrically conductive material; dc.c - the average grain size of the bulk medium; Sam. - adhesion (tearing strength) of electrically conductive material; Ss - adhesion (tear strength) of the flowing medium; Sam - module of all-round compression of electrically conductive material; Gc.c bulk compression module, and the maximum cavity diameter is 2-3 times the size of the dielectric plate.